JPS6139952A - Method for measuring width of pit of optical disc master disc - Google Patents

Abstract

PURPOSE:To measure contactlessly a pit width of an optical master disc with high accuracy by irradiating obliquely laser light on the optical master disc, reflecting the light and detecting the difference of the polarized state between the incident light and the reflected laser light. CONSTITUTION:The laser light irradiated from a laser light source 22 is subjected to straight line polarization, and when the light is transmitted through a 1/4 wavelength plate 24, the light is subjected to elliptic polarized light, is irradiated obliquely from a photo-resist layer of the master disc 20 and reflected therein. The reflected laser light is detected by a detector 28 via an analyzer 26. The difference in the polarized state between the incident light and the reflected laser light is detected by the detector 28 and converted into the layer thickness. Since lots of pits are irradiated once by the irradiated light, the layer thickness obtained is not the thickness of the photo-resist layer itself and is a value changing depending on the quantity of pit width A. The pit width is specified by the layer thickness measured by an ellipsometer depending on the relation. Thus, the pit width of an optical master disc is measured contactlessly with high accuracy.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a method for measuring groove width of an optical disk master.

(Prior Art) Since an optical disc master should serve as a standard for optical disc production, it is necessary to produce it accurately as designed.

As shown in FIG. 2, an optical disc master generally has a transparent photoresist 12 provided on a substrate 10 such as a glass plate, and the surface of the photoresist 12 has grooves with a cross-sectional shape as shown in FIG. is formed.

In FIG. 2, the length indicated by the symbol P is called the pitch of the groove, the length indicated by the symbol □ is called the depth of the groove, and the length indicated by the symbol A is called the groove width.

By the way, with recent master disk manufacturing techniques, high precision can be obtained relatively easily with respect to the pitch P and the groove, but the groove width A has relatively large variations due to manufacturing reasons.

Therefore, in order to check the quality of a prototype optical disc master, it is necessary to accurately measure the groove width A.

In order to accurately measure the groove width A, conventionally known methods include observing the cross-sectional shape using a scanning electron microscope and using a contact type surface roughness meter. This requires a destructive inspection, and in the latter case, the stylus comes into contact with the master disc, causing damage to the master disc. Therefore, masters measured using these measurement methods will no longer be paired.

(Objective) Therefore, an object of the present invention is to provide a groove width measuring method that can accurately measure the groove width in an optical disc master without contacting the master.

(composition) One aspect of the present invention will be explained below.

The features of the present invention are as follows.

That is, a laser beam is irradiated onto the optical disk master from an oblique direction and reflected. Then, the difference in polarization state between the incident laser light and the reflected laser light is detected, and the groove width is determined from this difference in polarization state.

When a layer of a transparent material is formed on a substrate such as glass and light is irradiated onto the surface of the transparent material and reflected, the polarization state of the reflected light will be different from the polarization state of the incident light.

The difference in polarization state between incident light and reflected light depends on the layer thickness of the transparent material layer.

Therefore, it is possible to know the thickness of the transparent material layer based on the difference in polarization state between the incident light and the reflected light. An ellipsometer is known as a device that uses this principle to measure the layer thickness of a transparent material layer on a substrate. using an ellipsometer.

It is possible to measure the thickness of a transparent material layer with IA accuracy.

The illumination light from the ellipsometer is focused on the optical disc master into a spot with a diameter sufficiently small compared to the groove width, and the optical disc master is scanned with this illumination light in a direction perpendicular to the groove. If this is done, the groove width should be able to be measured from the variation in the thickness of the photoresist layer between the groove part and the optical groove part, but the groove width A should be 0.40 to 0.60μ.
Since the diameter of the groove is extremely small, on the order of m, it is difficult to focus the illumination light into a sufficiently small spot diameter even compared to such a small groove width, and it is currently difficult to measure the groove width using the method described above. .

However, the inventors have discovered that the groove width in an optical disk master can be measured with high precision without particularly reducing the spot diameter of the illumination light that irradiates the photoresist surface of the master.

This will be explained below using a specific example.

In FIG. 1, reference numeral 20 indicates an optical disc master.

The laser light emitted from the laser light source 22 is linearly polarized, and when it passes through the 174-wave plate 24, it becomes elliptically polarized light, which is obliquely irradiated from the photoresist layer side of the master 20 and reflected. The incident light is.

The beam is a parallel beam with a cross-sectional diameter of about 1+nm, and the incident angle ψ is usually set to about 60 to 70 degrees. Therefore, approximately several hundred to one thousand grooves are irradiated with the incident laser beam.

The reflected laser light is detected by a detector 28 via an analyzer 26. Between incident laser light and reflected laser light,
The polarization states are different, and the difference in polarization state is detected by the detector 28, and the difference in polarization state is converted into layer thickness.

When an optical disc/master disc is irradiated with an incident laser beam, the irradiation light irradiates a large number of grooves at once, as described above, so the ``layer thickness value'' obtained as described above is based on the photo of the master disc. It does not give the thickness of the resist layer itself.

However, this "layer thickness value" changes depending on the size of the groove width in the master. This point was newly discovered by the present inventor.

In FIG. 3, the horizontal axis indicates the groove width of the groove on the master disc. The vertical axis indicates the value obtained by converting the difference in polarization and optical state into a layer thickness value. The two are connected by the relationship shown in the figure. From this relationship, the groove width can be specified by the layer thickness value "'" given as the measurement result of the ellipsometer.

This curve 3-1 in FIG. 3 is called a characteristic line.

The characteristic line naturally changes if the pitch of the grooves on the master disk or the depth of the grooves changes, but the qualitative tendency is the same as that of curve 3-1.

Therefore, various characteristic lines are stocked in advance with various pitches and depths. In the measurement, first, the characteristic line is specified by knowing the pitch and depth.

Next, a measured value is given by an ellipsometer, and the measured value given as a "layer thickness value" is converted into a groove width value using the characteristic line specified above.

Operations from measurement with an ellipsometer to calculation of groove width can be automated using a macrocomputer.

Finally, the accuracy of the groove width measured by this method will be explained.

As an example, if we take characteristic line 3-1, the change in groove width is 0.15.
The "layer thickness value" changes by about 120 A compared to about μm. As mentioned above, although the ellipsometer can read up to IA, the accuracy of the groove width value measured by this method is on the order of 0.001 μm regarding the characteristic line 3-1. Experiments confirmed that this result is general.

(Effects) As described above, according to the present invention, it is possible to provide a novel method for measuring groove width in an optical disc master. In this method, the measurement is performed without contacting the master disc, so that the optical disc master is not damaged by the measurement. Also, the measurement accuracy is high. Note that there are various types of ellipsometers, and the present invention is not limited to the one shown in FIG. 1, and various types of ellipsometers can be used.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram for explaining an optical disc master, and FIG. 3 is a diagram for explaining the present invention.

Claims (1)

[Claims] A groove in an optical disc master, characterized in that the groove width in the optical disc master is measured by irradiating a laser beam on the optical disc master from an oblique direction and reflecting it, and detecting the difference in the polarization state between the incident laser beam and the reflected laser beam. Width measurement method.